This is the U.S. National Stage of International Application No. PCT/JP03/07631, filed on Jun. 16, 2003, which relies for priority on Japanese Patent Applications Nos. 2002-179785. filed Jun. 20, 2002 and 2002-310967, filed Oct. 25, 2002, the contents of all of which are incorporated herein by reference in their entireties.
1. Field of the Invention
This invention relates to a rotor for a permanent magnet motor of the outer rotor type which includes a number of annularly arranged permanent magnets for formation of magnetic poles.
2. Description of the Related Art
FIGS. 18 and 19 illustrate a part of a rotor for a conventional permanent magnet motor of the outer rotor type in which a rotor is disposed around a stator. As shown, a rotor 10 comprises a frame 1 made from a magnetic material and including a disc-like main plate 1a and an annular circumferential wall 1b located around the main plate 1a, and a plurality of permanent magnets 2 arranged on an inner circumferential face of the wall 1b for the purpose of forming magnetic poles. A ring member 4 made from a magnetic material is disposed along an outer circumference of the wall 1b. The aforesaid frame 1, permanent magnets 2 and ring member 4 are integrally combined with one another by a synthetic resin 5. For example, Japanese Patent No. 3017953 discloses a rotor with the above-described construction.
The above-described rotor 10 is manufactured in the following method. A forming die 6 includes a lower die 6a and an upper die 6b as shown in FIG. 20A. The permanent magnets 2 are inserted into a recess 7 formed in the lower die 6a. The recess 7 is formed into an annular configuration according to a shape and the number of the permanent magnets 2. The frame 1 is then put over the permanent magnets 2 inserted in the recess 7, and the ring member 4 is further disposed along the outer circumference of the frame.
Subsequently, the upper die 6b is put onto the lower die 6a so that the forming die 6 is closed as shown in FIG. 20B. A cavity 8 defined between the upper and lower dies 6b and 6a is filled with a synthetic resin 5 in the molten state. When the synthetic resin 5 has been hardened, the upper die 6b is removed and the rotor 10 is taken from the lower die 6b. Thus, a number of permanent magnets 2 are integrally combined with the frame 1 by the synthetic resin in the annularly arranged state.
In the above-described rotor 10, however, the recess 7 needs to be provided in the lower die 6a in order that the permanent magnets 2 may be prevented from being displaced during filling the interior of the die 6 with the synthetic resin 5. Accordingly, the configuration of the lower die 6a is complicated.